MILTONJ. ALLENAND ALSOPHH. CORWIN
114
two methyl substituents in the position ortho to the carboxyl group. TABLE \-
EFFECTOF METHYLSUBSTITUENTS OY
THE
KATE OF
ESTERIFICATION OF BENZOIC ACIDI S hfETHASOI, kro X 105, I! Acid liters moles-1 sec - 1 cal. mole''
Benzoic 21.7 Benzoic" 19 2 p-Toluic" 19.7 21.7 nt-Toluic" 3,5-Dimethylbenzoic "1 f l 3,4-Dimethylbenzoic 1 i 4 o-Toluic" A 41 2,4-Dimethylbenzoic .i X7 2,Ei-Dimethylbenzoic 3 (59 2,6-Dimethylbenzoic S o reaction 'I Data of Hartman and Borders, ref. 2 .
14,600 15,500 13,800 14,201)
14,900 16,000 14,400
15,500 15,400
It is quite obvious that the acids fall into three groups, depending on the number of substituents in the ortho position, and that the rate of reaction is decreased with increasing number of such substituents. The results for benzoic acid reported here give an activation energy for the esterification
Yol. i2
of benzoic acid which is 900 calories lower than that reported by Hartman and Borders. With this revision, there seems to be little evidence for lowering of the activation energy by methyl substituents. On the contrary, there seems to be a slight increase when a methyl group is substituted in the ortho position. One would estimate that the activation energy for the 2,6-substituted acid is much greater than any value recorded in Table V. It s e e m probable that the retarding influence of the 2-methyl groups is primarily steric in nature, and is much the sanie as that of &methyl substituents in aliphatic acids.
Summary The kinetics of the acid-catalyzed esterification in methanol of benzoic acid and of the dimethylsubstituted benzoic acids have been studied. Velocity constants and activation energies for these reactions have been compared with similar values for the toluic acids. It has been shown that the relative rates of esterification are influenced by substitution in the ortho, but not in the meta and para position. KNOXVILLE,TENNESSEE RECEIVED OCTOHER 10, 1949
[ CONTRIBUTIOS FROM THE CHEMICAL I~ABORATORIESOF THE JOHNS HOPKINS UNIVERSITY]
The Electrolytic Reduction of RY MILTONJ. ALL EN?^^"
Numerous studies have been undertaken in the past to determine the effects of electrolytic reduction on ketones. Usually the reduction proceeds to a pinacol, an alcohol, a hydrocarbon or a mixture of both pinacol and alcohol. Of these reactions, the formation of a hydrocarbon is not usually a continuatibn of the secondary alcohol formation, as secondary alcohols are not easily reduced by electrolytic method^.^ There is no doubt that the reaction which takes place depends upon the electrode material and the type of electrolyte used. Elbs and Brand4 found that in alkaline solution, using a lead cathode, the aliphatic and aromatic ketones are reduced to the corresponding secondary alcohol, whereas in acid solution, a mixture of pinacol arid alcohol is obtained. Escherich and lloestj found that Slichler ketone yields the pinacol with a copper cathode, while both pinacol and alcohol are formed i n almost equal amounts at a nickel cathode.
* Harvard University Ph D
1'132
(1) ThL. investigation was supported, in p a t , b) d research grant awarded M. J. A., by the National Cancer Institute of the National Institutes of Health, U. S. Public Health benice. (2) (a) Research Fellow, National Cancer In,titute, 1947-1949; (b) from the Ph.D. dissertation of Milton J Allen, T h e Johnz Hopkins University, June, 1949 (3) Tafel, Z.EZckfrochcm , 11, 973 (1'111) (4) Elbs and Brand, ibid , 8, 783 (1902) ( 5 ) Escherich and Mord, abrd 8, R W (1902)
AND
p-Aminoacetophenonel
ALSOPHH. CORWIN*
The prime purpose of this investigation was to study the change in products resulting from a change in experimental conditions, using d single type of cathode material, in an attempt to find the conditions which would give a maximum yield of 2,3-bis-(p-aminophenyl)-2,3-butanediol.
Experimental The apparatus used in this work was similar t o that described by Lingane,6 with the exception that cathode potentials as high as six volts and currents as high as 20 amperes were provided for. Essentially, this apparatus will give automatically controlled impressed voltage to secure constant cathode potential. Two cells were developed for both small (25-50-ml.) and larger (400-800ml.) quantities of material (Fig. l a and lb). In the experiments to be discussed, the p-aminoacetophenone was dissolved in the desired solution and placed in the cathode chamber. A blank solution which excluded the ketone was placed in the anode compartment. The two compartments were separated by a cellophane membrane.' Table I gives some experimental results using a carbon anode and a mercury cathode.8 A smooth platinum anode and a mercury cathode were used in the experiments listed in Table 11. Most of the experiments were performed with diluted hydrochloric acid as the electrolyte, as the pinacol dihydrochloride was the desired product. The alcohol was isolated from the mother liquor after filtering off the pinacol. The solvent was removed, the (6) Lmgane, Ind. Eng. Chcm., Anal. Ed., 11, 332 (1845).
( 7 ) Purchased from the Visking Corp., Chicago, Ill. [ h ) Ller
